The present invention relates to an electrostatographic apparatus such as an electrostatic copying machine comprising an improved means for removing residual toner substance from a photoconductive member in the form of a drum, belt or the like.
In a typical electrostatic copying machine, a photoconductive member such as a drum is electrostatically charged and radiated with a light image of an original document, forming an electrostatic image through localized photoconduction. A dry toner substance is applied to the drum which forms a visible toner image thereon. The toner image is transferred and fixed to a sheet of copy paper to provide a permanent copy of the original document.
However, it is impossible in practical application to transfer all of the toner substance to the copy sheet, and a residual amount always remains. This residual toner substance must be removed from the drum prior to a subsequent copying operation to prevent double printing. From an economic standpoint, it is desirable to recycle rather than discard the residual toner substance after remove from the drum.
Various means have been proposed heretofore to remove residual toner substance from a drum and return the same to the developing unit of the copying machine. All such prior art means are rather complicated, and disproportionally increase the overall size and cost of the copying machine.
Whereas residual toner return in copying machines utilizing liquid toner is rather simple due to the fact that liquid toner readily flows downwardly through conduits and the like under the force of gravity, such return of dry powdered toner substance is hampered by the forces of dry friction, electrostatic and magnetic attraction, etc., even if air pressure or vacuum is utilized to facilitate movement.
In one known electrostatic copying machine a fur brush is used to remove the residual toner substance from the drum and a vacuum pump sucks the toner from the brush and returns the same to the developing unit through a conduit system. Such an arrangement, in addition to the drawbacks mentioned hereinabove, invites contamination of the toner substance due to accumulation of dirt and dust on the fur brush.
Another prior art expedient for residual toner removal and recycling utilizes a scraper blade to remove the toner from the drum and a conveyor comprising an elongated worm screw to return the toner substance to the developing unit. The conveyor may have one or more sections comprising endless belts or chains. This arrangement is especially disadvantageous due to excessive complexity, size and cost.